An undesired hole may be formed in a metallic article during fabrication or service. Such an undesired hole is most common in relatively thin sheets of the metallic material. For example, during fabrication a hole may be unintentionally punched in a sheet structure or produced by a joining process. During service, holes may result from environmental causes such as burning or impacts of rocks or the like. Holes may also result from hostile penetrations from sources such as a bullet or other projectile. Existing holes also may become oversized or otherwise damaged due to wear, corrosion, or other in-service conditions.
In many cases, the extent of damage associated with the hole is not too great, and the hole may be repaired. In one common approach, the hole is patched with a sheet of a material attached, as by welding, overlying the hole. This patch thickens the sheet and alters its aerodynamic properties, and also results in reduced strength in the neighborhood of the hole and leaves a stress concentration having an increased propensity for premature failure.
In another approach, the hole is welded shut, as for example by gas tungsten arc welding of a hole in an aluminum alloy. Weld repair can lead to significant distortion of the shape and dimensions of the article, particularly for thin sheets. Various types of support fixtures and chill blocks are used to reduce the distortion, but such tooling significantly increases the cost of the repair. Additionally, the quality of the weldments in thin workpieces is suspect, so that the strength of the welded structure is compromised. Most materials shrink when they solidify, leaving porosity in the weldment. Gas bubbles in the weldment also produce porosity. The porosity reduces the mechanical properties of the weldment and thence of the welded structure. Another important disadvantage is that the quality of conventional weldments is highly dependent upon the skill of the welder or the setup of an automatic welding machine, so that there may be inconsistency from weld to weld.
There is a need for an improved approach to the repair of holes in metallic articles, particularly thin sheet articles. The present invention fulfills this need, and further provides related advantages.